Why EF navigation property return null?

Question

I have two model 1)

public class Indicator
{
    public long ID { get; set; }
    public string Name { get; set; }
    public int MaxPoint { get; set; }
             


        

Answer 1

I experienced this issue, where navigation properites were not loaded, even when the Include statement was present.

The problem was caused by string-comparison differences between SQL Server and EF6 using .NET. I was using a VARCHAR(50) field as the primary key in my customers table and also, as a foreign key field in my audit_issues table. What I did not realize was that my keys in the customers table had two additional white space characters on the end; these characters were not present in my audit_issues table.

However, SQL Server will automatically pad whitespace for string comparisons. This applies for WHERE and JOIN clauses, as well as for checks on FOREIGN KEY constraints. I.e. the database was telling me string were equivalent and the constraint passed. Therefore I assumed that they actually were exactly equal. But that was false. DATALENGTH of one field = 10, while the DATALENGTH of the other = 8.

EF6 would correctly compose the SQL query to pull the foreign key related fields and I would see them both in the generated Sql query and in the results. However, EF6 would silently fail when loading the Navigation Properties because .NET does not consider those strings equal. Watch out for whitespace in string-type foreign key fields!.